have at least used alcohol in their lifetime because substance-abstinent individuals are considered phenotypically unknown; i.e., they may have a high genetic liability for addiction, but the absence of any substance use would preclude their progression to dependence. Blood samples for DNA analysis were collected from each subject and submitted, together with electronic phenotypic and genetic data, to the National Institute on Drug Abuse (NIDA) Center for Genetic Studies. The study obtained informed consent from all participants and approval from the appropriate institutional review boards.
